1. Field of the Invention
The present invention relates to a rubber mixture, to a process for its preparation and to its use.
2. Description of the Related Art
It is known to use silanes as adhesion promoters. For example, aminoalkyltrialkoxysilanes, methacryloxyalkyltrialkoxysilanes, polysulfanealkyltrialkoxysilanes and mercaptoalkyltrialkoxysilanes are used as adhesion promoters between inorganic materials and organic polymers, as crosslinkers and surface-modifying agents (E. P. Plueddemann, “Silane Coupling Agents”, 2nd Ed. Plenum Press 1982).
These adhesion promoters, or coupling or bonding agents, form bonds both to the filler and to the elastomer and accordingly effect good interaction between the filler surface and the elastomer.
DE 22 55 577 dislcoses that the use of commercially available silane adhesion promoters having three alkoxy substituents on the silicon atom leads to the release of considerable quantities of alcohol during and after binding to the filler. Because trimethoxy- and triethoxy-substituted silanes are generally used, the corresponding alcohols, methanol and ethanol, are released in considerable quantities.
DE 10015309 discloses that the use of a mercaptosilane in combination with a long-chain alkylsilane in rubber mixtures leads to increased reinforcement and a reduced hysteresis loss. The alkylsilane is necessary to ensure that the rubber mixture can be processed reliably.
It is further known that methoxy- and ethoxy-substituted silanes are more reactive than the corresponding long-chain alkoxy-substituted silanes and accordingly are able to bind more rapidly to the filler, so that the use of methoxy and ethoxy substituents cannot be dispensed with from a technical and economic point of view.
From DE 10137809 there are known organosilicon compounds of the general formula
                or of the general formula        
                wherein R is a methyl or ethyl group,        the substituents R′ are identical or different and are a C9-C30 branched or unbranched monovalent alkyl or alkenyl group, aryl group, aralkyl group, branched or unbranched C2-C30 alkyl ether group, branched or unbranched C2-C30 alkyl polyether group,        R″ is a branched or unbranched, saturated or unsaturated, aliphatic, aromatic or mixed aliphatic/aromatic divalent C1-C30 hydrocarbon group,        X is NH(3-n) where n=1,2,3 and m=1, O(C═O)—R′″ where n=1 and m=1, SH where n=1 and m=1, S where n=2 and m=1-10 and mixtures thereof, S(C═O)—R′″ where n=1 and m=1 or H where n=1 and m=1, where R′″ is a C1-C30 branched or unbranched alkyl or alkenyl group, aralkyl group or aryl group.        
DE 10223658 discloses organosilicon compounds of the general formula
                wherein R is a methyl or ethyl group,        the substituents R′ are identical or different and are a C9-C30 branched or unbranched monovalent alkyl group,        R″ is a branched or unbranched, saturated or unsaturated, aliphatic, aromatic or mixed aliphatic/aromatic divalent C1-C30 hydrocarbon group, R′ is a mixture and the proportion of one component of the mixture is from 10 to 50 mol. %.        
Disadvantages of the known rubber mixtures containing mercaptosilanes having long-chain alkoxy groups are the short incubation time and the short Mooney scorch time, which do not ensure reliable processability.
From WO 03/020813 it is known that the Mooney scorch time of silica-containing rubber mixtures can be prolonged by dispensing with the addition, customary in the case of silica-containing rubber mixtures, of diphenylguanidine while at the same time increasing the amount of added thiuram disulfide and at the same time adding a polyalkylene oxide. The addition of a polyalkylene oxide is disadvantageous, because it interferes with the crosslinking density (Technical Report TR 818 of Degussa AG).